Hitherto, there have been developed disc cartridges of a type which comprises a magnetic disc which includes a flexible disc base having a magnetic layer lined thereon and a cartridge body which includes upper and lower body halves coupled to rotatably install therein the magnetic disc.
On an inner surface of each of the upper and lower body halves of the cartridge body, there is arranged a protection sheet made of a nonwoven fabric cloth or the like. The protection sheet arranged on the inner surface of the upper body half is partially protruded toward the magnetic disc by a plurality of comb-shaped projections formed on the inner surface of the upper body half. While, the protection sheet arranged on the inner surface of the lower body half is partially protruded toward the disc cartridge by a lifter, made of a thin blade spring, which is arranged on the inner surface of the lower body half at a position facing the projections of the upper body half. That is, due to the projections and the lifter, respective portions of the protection sheets arranged on the inner surfaces of the upper and lower body halves are protruded toward each other by such a degree as to contact the signal recording surfaces of the magnetic disc.
When the disc cartridge having the above-mentioned construction is put into a disc player and the magnetic disc in the cartridge body is chucked and driven by a disc driving mechanism of the disc player, the protruded portions of the protection sheets contact the rotating magnetic disc to remove dust therefrom.
A larger portion of each projection sheet other than the protruded portion functions to prevent the signal recording surfaces of the magnetic disc from directly contacting with hard inner surfaces of the cartridge body and from being damaged therefrom.
In the above-mentioned disc cartridge wherein by positively contacting the protection sheets with the magnetic disc, dusts on the magnetic disc can be removed, the dusts removed from the magnetic disc are caught by the protection sheets and attached thereto. If under this condition the magnetic disc is rotated, it tends to occur that the magnetic disc is damaged by the dust attached to the protection sheets.
In the above-mentioned disc cartridge, due to provision of the projections and the lifter, parts of the protection sheets are protruded toward the magnetic disc to contact therewith. Thus, load produced when the magnetic disc is rotated is increased. In a disc player by which the above-mentioned cartridge disc is played, there is a need of using a large-sized driving motor, as a part of a disc driving mechanism, for generating a larger driving torque for obtaining a stable rotation of the magnetic disc.
Furthermore, when, in the above-mentioned disc cartridge, the upper and lower body halves of the cartridge body are subjected to deformation such as warping or the like, it tends to occur that, due to provision of the projections and the lifter, the protection sheets are strongly pressed against the magnetic disc thereby to increase the load needed for driving the magnetic disc.
When the load of the magnetic disc is increased, the driving torque is also increased, which induces application of a marked load to the driving motor of the disc driving mechanism thereby inducing a possibility of having an unstable rotation of the magnetic disc.
In a magnetic disc with a high density recording capacity, the rotation speed of the disc is determined high. With increase of the rotation speed of the magnetic disc, the friction between the magnetic disc and the protection sheets contacting the magnetic disc increases, which tends to cause a damage of the signal recording surfaces of the magnetic disc. In order to rotate the magnetic disc at a higher speed, it is necessary to increase the rotation speed of the driving motor of the disc driving mechanism. When, in the driving motor, the rotation speed increases, the driving torque becomes reduced. Thus, a stable rotation of the motor is not obtained even if increase in the load applied to the magnetic disc is just a small and thus in this case, the magnetic disc can be rotated at a desired rotation speed. Furthermore, in this case, appropriate recording and replaying of information signal is not expected from the magnetic disc.
An object of the present invention is to provide a disc cartridge which can remove dusts from a disc by using rotation of the disc without aid of members which contact the disc.
Another object of the present invention is to provide a disc cartridge wherein a disc is prevented from directly contacting with a cartridge body so that the disc is protected.
Still another object of the present invention is to provide a disc cartridge wherein rotation of a disc is carried out without applying a drive motor, which constitutes a disc drive mechanism, with a marked load.
Further object of the present invention is to provide a disc cartridge which can protect a disc installed in a cartridge body and assure a stable rotation of the disc in the body.
Further object of the present invention is to provide a disc cartridge which can discharge dusts from a cartridge body to the outside and prevent invasion of dusts into the cartridge body from the outside.